Compositionality, Hierarchy and Recursion in Language. A Case Study in Fluid Construction Grammar

In this thesis it is argued that a number of universal features of human lan-guages can be explained as being emergent properties of the complex dynamicsgoverning the establishment and evolution of a language in a population of in-terlocutors on an inter-generational time scale, rather than being the result ofa genetic selection process leading to a specialized language faculty that im-poses those features upon language or than being a cross-generational culturalphenomenon.

In particular, I will focus on compositionality, hierarchy and recursion, gen-erally acknowledged to be universal features of human languages. Together, bycombining words into hierarchical phrases which can then recursively be com-bined into larger phrases, they allow the construction of an unlimited numberof sentences using only a limited number of words.

There have been two major hypothesis about why all languages share thesefeatures: nativism and iterated learning. Unfortunately, in recent years, the evi-dence for humans possessing a unique and genetically encoded faculty dedicatedto language has become increasingly small. The iterated learning hypothesis isalso unsatisfactory, mainly because it neglects to see language as a complexadaptive system that is being shaped by language users as they are attemptingto communicate.

It is argued that the mere urge for successful communication can explainwhy language becomes compositional, hierarchical and recursive: because thesefeatures allow the re-use of already acquired bits of language which in turnincreases the chance that at least part of the message is conveyed. To supportthis claim, an experiment is presented in wich a number of artificial agentsbootstrap a communication system. It is shown that although the agents arenot innately wired or biased towards recursive language and without any flowin the population, compositional and recursive language indeed can emerge.